the response by joecomotion here are key, you guys should put this in the quick start documentation. I used the ymdt put APPNAME, and my app loaded well, I advise you guys to tell others here is the forum post, please make it more public http://developer.yahoo.com/forum/Yahoo-Mail-Application-Platform/can-not-create-sample-app/1301079475000-8bf57769-f87a-3d94-8094-b0c1d1baa2c8
QUOTE
(Houyhnhnm @ 9 Oct 2011 4:24 PM)I get this message when I try to lead my app
Sorry, but the application "HIAMMP Houyhnhnm Internet Archive MEdia in Mail Player" is currently unavailable. Please try again later.
here is the former posting concerning this issue.